The thalamus is a complicated structure that relays and processes motor-related information from the basal ganglia to the cerebral cortex. It also sends highly topographic and massive projections back to the striatum, the primary input nucleus of the basal ganglia. However, the circuitry of the thalamostriatal system, and its role in regulating basal ganglia function during normal movement and during disease states, such as Parkinson's Disease, is poorly understood. The objective of this research proposal is to characterize the microcircuitry of the thalamostriatal projection, which arises from the ventral anterior (VA) and ventral lateral (VL) motor thalamic nuclei using tract tracing, confocal microscopy, and immunocytochemical electron microscopy techniques. The first aim will determine the synaptology of VA/VL thalamostriatal afferents, and the second aim will investigate the differential innervation of VA/VL afferents with the direct and indirect pathways of the basal ganglia. Knowledge gained from these experiments will advance our understanding of interactions between the thalamus and the basal ganglia and provide valuable information on the mechanisms by with this interaction may contribute to the normal and pathological function of the basal ganglia.